GHRP-6 — identity, handling and published literature

GHRP-6 is a synthetic six-residue growth hormone secretagogue peptide, supplied as a lyophilised powder for laboratory use; it is not part of the NovoVita catalogue and is included here because the library documents the compound class rather than the product range.

Presentation and physical properties

GHRP-6 is a synthetic hexapeptide carrying a C-terminal amide. It is not a fragment or analogue of any human protein: the sequence was designed from structure–activity work on opioid peptides rather than derived from an endogenous hormone, and it bears no sequence relationship to ghrelin despite the two acting at the same receptor. Two of the six residues are D-enantiomers — D-tryptophan at position 2 and D-phenylalanine at position 5 — which is the principal reason the molecule resists the proteases that would rapidly degrade an all-L hexapeptide.

The material presents as a white to off-white lyophilised solid, typically a low-density cake or powder. It is supplied in practice as the acetate salt rather than as the free base, so the mass in a vial includes acetate counter-ion and residual water; peptide content by weight is therefore lower than the nominal figure, commonly in the region of 80–90 per cent depending on the manufacturer’s salt form and lyophilisation. The free base has a molecular weight of 873.0 g/mol.

The peptide is freely soluble in water and in aqueous buffers at neutral pH. Its two tryptophan residues make it appreciably light-sensitive in solution and give it a usable ultraviolet absorbance near 280 nm. The lyophilised solid is hygroscopic and will take up atmospheric moisture if a vial is opened cold.

Reconstitution arithmetic

Reconstitution is a dilution calculation and nothing more. The concentration of the resulting solution is the mass of peptide in the vial divided by the volume of diluent added:

Concentration (mg/mL) = vial mass (mg) ÷ diluent volume (mL)

Adding diluent does not change the quantity of peptide present — it changes only how much liquid that quantity is distributed through. The table below works this through for a nominal 5 mg vial at three diluent volumes. GHRP-6 is not supplied by NovoVita, so no house presentation exists; 5 mg is used here purely as a round figure for the arithmetic.

The final column expresses the same figures per 0.01 mL, that being one graduation on a 100-unit-per-millilitre syringe barrel. It is a unit conversion, not a recommendation of any quantity. Two arithmetical points are worth stating explicitly: the nominal vial mass is the salt mass, so the peptide mass is lower by the counter-ion fraction noted above, and any figure calculated from the label is therefore an upper bound on peptide content unless a certificate of analysis states peptide content directly. Second, a small volume of diluent produces a concentrated solution in which measurement error at the syringe is proportionally larger.

Storage and stability

Lyophilised GHRP-6 is stable for extended periods at −20 °C or below, kept sealed, desiccated and protected from light. Short transport periods at ambient temperature are tolerated by the dry solid, which is why the material is routinely shipped without a cold chain; this tolerance does not extend to solution.

Vials should be brought to room temperature before opening. Opening a cold vial draws in humid air that condenses on the cold solid, and a lyophilised peptide that has taken up water loses the storage stability the drying step conferred.

Once reconstituted the peptide is far less stable. Aqueous solutions are conventionally held at 2–8 °C and treated as short-lived, with light excluded because of the tryptophan content. Repeated freeze–thaw cycling is a recognised degradation route for peptides in solution and is avoided by dividing a reconstituted stock into single-use aliquots at the outset. Bacteriostatic diluents containing benzyl alcohol are used where a solution is to be entered more than once; sterile water offers no such protection.

The peptide’s resistance to enzymatic breakdown has been characterised directly. A 2023 study of the enzymatic and serum stability of GHRP- and GHRH-related peptides exposed synthesised GHRP-4, GHRP-5 and GHRP-6 to human blood, trypsin and chymotrypsin, and reported that GHRP-6 was stable to both enzyme and blood treatment — sufficiently so that the authors proposed it as an in-house internal standard for the quantification of other peptides in biological matrices [19]. That stability is a consequence of the two D-residues and the C-terminal amide.

Analytical identity

The identity of GHRP-6 is established by mass and by sequence. From the molecular formula C₄₆H₅₆N₁₂O₆, the average molecular weight is 873.0 and the monoisotopic mass is 872.44 Da; under positive-ion electrospray the singly protonated species appears at m/z 873.45 and the doubly protonated species near m/z 437.23. The doubly charged ion is generally the more useful, the molecule carrying two readily protonated basic sites in the histidine imidazole and the lysine side chain.

Purity is assessed by reversed-phase HPLC, typically on a C18 stationary phase with a water–acetonitrile gradient and trifluoroacetic acid as ion-pairing agent, with detection at 220 nm for the peptide bond and at 280 nm for the tryptophan residues. The 280 nm channel is diagnostic here rather than merely confirmatory, since two of six residues are tryptophan and the ratio of the two absorbances is itself an identity check.

Mass spectrometry alone cannot distinguish GHRP-6 from a stereochemical impurity: a preparation in which D-tryptophan has been replaced by L-tryptophan has an identical formula and identical mass, and is separable only chromatographically. This matters because the D-residues are what confer the stability described above. Structure–activity work using positional scanning of the GHRP-6 sequence has mapped which residues and which stereocentres are load-bearing [14].

Analytical methods for GHRP-6 are well developed outside the research-chemical setting because anti-doping laboratories require them. A 2011 method paper established liquid chromatography–mass spectrometry determination of growth hormone-releasing peptides and their major metabolites in human urine for doping control [16], and subsequent work has addressed solid-phase extraction of small peptides from urine [20] and the structure–activity relationships underlying peptidic secretagogue detection. A 2019 analysis of seized doping material identified glycine-modified growth hormone secretagogues [18] — a reminder that material sold under a peptide name is not always that peptide, and that analogues designed to evade a mass-spectrometric target list circulate in this market.

What the published literature investigated

GHRP-6 has an unusually long literature for a research peptide. It was first described in 1984 and remained a standard pharmacological tool through the 1990s, so the published record spans four decades and includes a substantial body of controlled human work.

In vitro and receptor pharmacology

The compound was introduced by Bowers and colleagues in 1984, who reported that the synthetic hexapeptide acted on the pituitary to release growth hormone in rat pituitary cell preparations and in vivo, and reported that release as specific to growth hormone among the pituitary hormones assayed [1]. The same year, a separate group reported the effects of growth hormone-releasing peptides on secretion in perifused pituitary cells from adult male rats [2], and a 1985 study ran parallel comparisons of the hexapeptide against human pancreatic growth hormone-releasing factor-44 in rat primary pituitary cell monolayer culture [3]. That 1985 paper is also of identity interest: it carries the full sequence, His-D-Trp-Ala-Trp-D-Phe-Lys-NH₂, in its title.

The receptor question stayed open for over a decade. In 1996 a receptor in pituitary and hypothalamus functioning in growth hormone release was cloned and reported in Science [4], establishing that the growth hormone secretagogues acted through a distinct G-protein-coupled receptor rather than through the GHRH receptor. The endogenous ligand for that receptor was unknown until 1999, when ghrelin was identified as an acylated growth-hormone-releasing peptide isolated from stomach [5]. The order of events is worth noting: GHRP-6 was a synthetic ligand in use for fifteen years before the natural hormone whose receptor it occupies had been found, and the peptide functioned as the probe that led to both discoveries.

A second receptor interaction has been investigated separately. Work on azapeptide derivatives of GHRP-6 characterised the sequence as a ligand of the CD36 scavenger receptor, with structure–activity relationships mapped by solid-phase submonomer azapeptide synthesis [15]. This line of research has pursued analogues selective for CD36 over the growth hormone secretagogue receptor, deliberately separating the two activities.

Rodent and other animal models

A 2016 study in a rodent model reported that GHRP-6 administration was associated with accelerated wound closure and altered cosmetic outcome of experimental wounds relative to controls [13]. This sits within a wider preclinical programme, largely conducted by a single research group, investigating non-secretagogue actions of the peptide mediated through CD36 rather than through growth hormone release.

In the cardiovascular literature, azapeptide derivatives of GHRP-6 acting as selective CD36 ligands were reported in 2020 to have atheroprotective and atheroregressive effects in apolipoprotein E-deficient mice [17]. That study examined derivatives rather than GHRP-6 itself, and the distinction is material to how the result should be read.

Human studies

Human studies of GHRP-6 itself exist in quantity, and this should be stated plainly: they are studies of this exact substance, not of a parent protein or a related analogue. Most are small, acute, single-administration endocrine challenge studies conducted in the 1990s, and their purpose was largely to characterise the growth hormone axis rather than to establish therapeutic effect.

The foundational human study, published in 1990, reported that the peptide stimulated growth hormone release in normal men and acted synergistically with growth hormone-releasing hormone [6]. That synergy became the basis for a combined test protocol used in endocrine investigation. A 1998 randomised study subsequently reported that maximal stimulation required endogenous hypothalamic GHRH [9], clarifying that the peptide’s effect in humans is not purely pituitary.

A 1995 randomised controlled study in normal men reported that GHRP-6 stimulated sleep, growth hormone, ACTH and cortisol release [7]. This finding is important to the compound’s characterisation: the specificity for growth hormone reported in the original 1984 rat pituitary work does not hold in humans, where corticotroph activation is also observed. A 2003 randomised study reported that GHRP-6 stimulated cortisol and ACTH release in patients with Cushing’s disease, compared against DDAVP [11], and further studies examined responses in hypothyroidism [10] and across age groups, the latter reporting that the growth hormone response did not decline in late adulthood [8].

The most recent substantial human work is a Phase I pharmacokinetic study published in 2013 in nine male healthy volunteers, which administered single intravenous boluses at three levels and quantified plasma concentrations by a validated LC-MS method [12]. It reported a distribution half-life of 7.6 ± 1.9 minutes and an elimination half-life of 2.5 ± 1.1 hours, found that disposition was better described by a two-compartment than a one-compartment model, and noted atypical concentration spikes during the elimination phase in four of the nine subjects — an observation the authors flagged as requiring further investigation.

Two contemporaneous reviews summarise the state of the field as it stood at the end of the 1990s [21][22].

Evidence gaps and limitations

The size of the literature should not be mistaken for depth of evidence about outcomes.

No Phase II or Phase III efficacy trial of GHRP-6 has been completed for any indication in the United Kingdom, the European Union or the United States. The human record consists of acute endocrine challenge studies with participant numbers typically in single or low double figures, plus one Phase I pharmacokinetic study in nine volunteers. There is no registration-standard trial, no large randomised trial, no active-comparator trial, and no long-term study of any kind. Nothing in the human literature addresses repeated administration over weeks or months.

There is consequently no long-term safety dataset. The documented stimulation of ACTH and cortisol alongside growth hormone [7][11] means the compound is not endocrinologically selective in humans, and the consequences of sustained corticotroph stimulation have not been studied. Prolactin responses have also been reported in this compound class. The original claim of specificity derives from rat pituitary preparations [1] and does not transfer.

The cytoprotective and wound-healing literature is almost entirely preclinical, is concentrated in a small number of research groups, and has not been replicated in independent human trials. Several of the cardiovascular findings concern azapeptide analogues rather than GHRP-6 [17], and results obtained with a derivative selected for altered receptor selectivity are not evidence about the parent peptide.

The identification of ghrelin in 1999 [5] substantially reframed the field, and pharmaceutical development moved towards orally available non-peptide secretagogues and towards ghrelin analogues. GHRP-6 was not carried forward. Its diagnostic use in growth hormone axis testing has largely been superseded. The practical consequence is that the compound has neither the deep clinical dataset of a developed drug nor the currency of an active research target.

There is no pharmacopoeial monograph for GHRP-6 in the British, European or United States Pharmacopoeia. No compendial identity, purity or impurity specification therefore exists, and no reference standard is available against which a preparation can be qualified. Purity claims from any supplier rest on that supplier’s own methods.

Regulatory and standards position

GHRP-6 has never held a marketing authorisation in the United Kingdom, the European Union or the United States. It is not an approved or authorised medicine in any of those jurisdictions, is not listed in any national formulary, and no product containing it has been granted a licence for human or veterinary use.

In the United Kingdom it is not a controlled drug. It is not scheduled under the Misuse of Drugs Act 1971 or the Misuse of Drugs Regulations 2001, which distinguishes it from somatropin — a Class C controlled drug under Schedule 4 Part II — despite the two acting on the same hormonal axis. Its supply is nonetheless constrained: under the Human Medicines Regulations 2012 a product becomes a medicinal product where it is presented as having properties for treating or preventing disease, so the regulatory position of a given GHRP-6 preparation turns on how it is described rather than on the molecule. MHRA Guidance Note 8 sets out that test, and the principle that a claim rather than a composition creates a medicinal product by presentation is long-established in EU case law.

In the United States GHRP-6 is not an FDA-approved drug. It has been nominated for the FDA’s list of bulk drug substances that may be used in compounding under section 503A of the Federal Food, Drug and Cosmetic Act but has not been placed in the category that would permit such use, and FDA has restricted the compounding of growth hormone secretagogues generally. The composition of the 503A category lists has been revised repeatedly, most substantially from September 2023 onwards, and any statement about a specific category placement should be checked against the current FDA list rather than taken from secondary sources.

The anti-doping position is unambiguous and is the one place where GHRP-6 is named explicitly in a current regulatory instrument. The WADA 2026 Prohibited List places it in section S2, Peptide Hormones, Growth Factors, Related Substances, and Mimetics, which is prohibited at all times, both in-competition and out-of-competition. All substances in class S2 are non-Specified Substances. Within that section, GHRP-6 appears at S2.2.4, “Growth hormone releasing factors”, in the bullet covering GH-releasing peptides, listed alongside alexamorelin, examorelin (hexarelin), GHRP-1, GHRP-2 (pralmorelin), GHRP-3, GHRP-4 and GHRP-5. The same subsection separately names GHRH analogues including CJC-1293, CJC-1295, sermorelin and tesamorelin, and growth hormone secretagogues including anamorelin, capromorelin, ibutamoren (MK-677), ipamorelin, lenomorelin (ghrelin), macimorelin and tabimorelin.

That prohibition is enforceable in practice rather than nominal. Validated LC-MS methods for GHRP-6 and its urinary metabolites have been published since 2011 [16], routine solid-phase extraction procedures for small peptides from urine are established [20], and analysis of seized doping material has documented modified secretagogue analogues in circulation [18]. Any person subject to anti-doping regulation should treat possession as well as use as consequential.

Laboratory handling and safety

GHRP-6 is a biologically active compound with no established human safety profile for repeated administration and no occupational exposure limit. It should be handled as a potent research chemical of unknown toxicity.

Standard laboratory precautions apply: gloves, eye protection and a laboratory coat; handling of the dry powder in a manner that avoids generating airborne particulate, since a lyophilised solid disperses readily and a low-density cake can be disturbed by the act of opening the vial; no eating, drinking or storage of food in areas where the compound is handled; and washing of hands after handling. Weighing of the open solid is best carried out in a containment enclosure.

The material is hygroscopic, so vials are equilibrated to room temperature before opening and resealed promptly. Solutions are labelled with compound, concentration and date of reconstitution at the time of preparation; an unlabelled vial of clear solution is indistinguishable from any other and cannot be verified afterwards.

There is no antidote and no established treatment for accidental exposure. Waste, including unused solutions, contaminated sharps and empty vials, is disposed of through the laboratory’s chemical waste stream in accordance with local regulations, not through general waste or drains. Users should hold a COSHH assessment covering the compound before work begins, recognising that the absence of a comprehensive toxicological dataset is itself a finding that the assessment must address rather than a reason to omit one.

References

1. Bowers CY, Momany FA, Reynolds GA, Hong A. On the in vitro and in vivo activity of a new synthetic hexapeptide that acts on the pituitary to specifically release growth hormone. Endocrinology. 1984;114(5):1537–45. Rat pituitary cells in vitro and in vivo. PMID 6714155
2. Badger TM, Millard WJ, McCormick GF, Bowers CY, Martin JB. The effects of growth hormone (GH)-releasing peptides on GH secretion in perifused pituitary cells of adult male rats. Endocrinology. 1984;115(4):1432–8. In vitro, perifused rat pituitary cells. PMID 6148232
3. Sartor O, Bowers CY, Chang D. Parallel studies of His-DTrp-Ala-Trp-DPhe-Lys-NH2 and human pancreatic growth hormone-releasing factor-44-NH2 in rat primary pituitary cell monolayer culture. Endocrinology. 1985;116(3):952–7. In vitro, rat pituitary monolayer culture. PMID 3918849
4. Howard AD, Feighner SD, Cully DF, et al. A receptor in pituitary and hypothalamus that functions in growth hormone release. Science. 1996;273(5277):974–7. In vitro receptor cloning and expression. PMID 8688086
5. Kojima M, Hosoda H, Date Y, Nakazato M, Matsuo H, Kangawa K. Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature. 1999;402(6762):656–60. Rodent tissue isolation and characterisation. PMID 10604470
6. Bowers CY, Reynolds GA, Durham D, Barrera CM, Pezzoli SS, Thorner MO. Growth hormone (GH)-releasing peptide stimulates GH release in normal men and acts synergistically with GH-releasing hormone. The Journal of Clinical Endocrinology and Metabolism. 1990;70(4):975–82. Controlled clinical trial, human. PMID 2108187
7. Frieboes RM, Murck H, Maier P, Schier T, Holsboer F, Steiger A. Growth hormone-releasing peptide-6 stimulates sleep, growth hormone, ACTH and cortisol release in normal man. Neuroendocrinology. 1995;61(5):584–9. Randomised controlled trial, human. PMID 7617137
8. Micic D, Popovic V, Kendereski A, Macut D, Casanueva FF, Dieguez C. Growth hormone secretion after the administration of GHRP-6 or GHRH combined with GHRP-6 does not decline in late adulthood. Clinical Endocrinology. 1995;42(2):191–4. Randomised controlled trial, human. PMID 7734029
9. Pandya N, DeMott-Friberg R, Bowers CY, Barkan AL, Jaffe CA. Growth hormone (GH)-releasing peptide-6 requires endogenous hypothalamic GH-releasing hormone for maximal GH stimulation. The Journal of Clinical Endocrinology and Metabolism. 1998;83(4):1186–9. Randomised controlled trial, human. PMID 9543138
10. Pimentel-Filho FR, Ramos-Dias JC, Ninno FB, Façanha CF, Liberman B, Lengyel AM. Growth hormone responses to GH-releasing peptide (GHRP-6) in hypothyroidism. Clinical Endocrinology. 1997;46(3):295–300. Randomised controlled trial, human. PMID 9156038
11. Oliveira JH, Vieira JG, Abucham J, Lengyel AM. GHRP-6 is able to stimulate cortisol and ACTH release in patients with Cushing’s disease: comparison with DDAVP. Journal of Endocrinological Investigation. 2003;26(3):230–5. Randomised controlled trial, human. PMID 12809173
12. Cabrales A, Gil J, Fernández E, et al. Pharmacokinetic study of Growth Hormone-Releasing Peptide 6 (GHRP-6) in nine male healthy volunteers. European Journal of Pharmaceutical Sciences. 2013;48(1–2):40–6. Phase I clinical trial, human. PMID 23099431
13. Mendoza Marí Y, Fernández Mayola M, Aguilera Barreto A, García Ojalvo A, Bermúdez Alvarez Y, Mir Benítez AJ, Berlanga Acosta J. Growth Hormone-Releasing Peptide 6 Enhances the Healing Process and Improves the Esthetic Outcome of the Wounds. Plastic Surgery International. 2016;2016:4361702. Rodent wound model. PMID 27200188
14. Boutard N, Jamieson AG, Ong H, Lubell WD. Structure-activity analysis of the growth hormone secretagogue GHRP-6 by alpha- and beta-amino gamma-lactam positional scanning. Chemical Biology & Drug Design. 2010;75(1):40–50. In vitro structure–activity study. PMID 19954433
15. Sabatino D, Proulx C, Pohankova P, Ong H, Lubell WD. Structure-activity relationships of GHRP-6 azapeptide ligands of the CD36 scavenger receptor by solid-phase submonomer azapeptide synthesis. Journal of the American Chemical Society. 2011;133(32):12493–506. In vitro receptor binding. PMID 21692501
16. Thomas A, Höppner S, Geyer H, Schänzer W, Petrou M, Kwiatkowska D, Pokrywka A, Thevis M. Determination of growth hormone releasing peptides (GHRP) and their major metabolites in human urine for doping controls by means of liquid chromatography mass spectrometry. Analytical and Bioanalytical Chemistry. 2011;401(2):507–16. Analytical method, human urine. PMID 21298258
17. Frégeau G, Sarduy R, Elimam H, et al. Atheroprotective and atheroregressive potential of azapeptide derivatives of GHRP-6 as selective CD36 ligands in apolipoprotein E-deficient mice. Atherosclerosis. 2020;307:52–62. Rodent model, GHRP-6 derivatives. PMID 32721647
18. Gajda PM, Holm NB, Hoej LJ, Rasmussen BS, Dalsgaard PW, Reitzel LA, Linnet K. Glycine-modified growth hormone secretagogues identified in seized doping material. Drug Testing and Analysis. 2019;11(2):350–354. Analytical characterisation of seized material. PMID 30136411
19. González-López NM, Guerra-Acero-Turizo LM, Blanco-Medina I, et al. In-house standards derived from doping peptides: Enzymatic and serum stability and degradation profile of GHRP and GHRH-related peptides. Biomedical Chromatography. 2023;37(12):e5741. In vitro stability study. PMID 37688464
20. Semenistaya E, Zvereva I, Krotov G, Rodchenkov G. Solid-phase extraction of small biologically active peptides on cartridges and microelution 96-well plates from human urine. Drug Testing and Analysis. 2016;8(9):940–9. Analytical method, human urine. PMID 26472487
21. Ghigo E, Arvat E, Muccioli G, Camanni F. Growth hormone-releasing peptides. European Journal of Endocrinology. 1997;136(5):445–60. Review. PMID 9186261
22. Bowers CY. Growth hormone-releasing peptide (GHRP). Cellular and Molecular Life Sciences. 1998;54(12):1316–29. Review. PMID 9893708

Research use only

GHRP-6 is supplied for laboratory research use only. It is not a medicinal product, holds no marketing authorisation in the United Kingdom, the European Union or the United States, and is not authorised for human or veterinary use. It is not for diagnostic use, not for administration to humans or animals, and not for use in food or cosmetics.

Nothing in this entry is a recommendation to administer this compound, a statement that it treats, prevents or improves any condition, or guidance on quantity, route or frequency of administration. The reconstitution section describes dilution arithmetic and nothing further. Studies are reported as statements about what those studies examined and found; a published finding in a laboratory or trial setting is not a claim about what the compound does outside it.

GHRP-6 is not part of the NovoVita catalogue and is not available for purchase. This entry exists because the reference library documents the compound class and the published record, independently of what is stocked. Anyone subject to anti-doping regulation should note the WADA position set out above before handling this compound in any capacity.